Levistus's_Leviathan
5e Freelancer
I over-plan, but don't "over-prepare", if that makes any sense. Basically, I lay out the whole main plot for a campaign all the way to level 20+, with world-shaking consequences and awesome stories to tell . . . but then only make it through enough sessions to get to around level 5. I have multiple examples of doing this, and it's just really disappointing. (And the stupid pandemic contributed a lot to this.)My second weakness was and still is, a tendency to over prepare. I could prepare a whole campaign for level 1 to 20 only to see the group die at level 10... Now I still over prepare, but it is a lot less. I try to keep ahead for 2 to 5 levels only...
As for preparing for individual sessions, yeah, I basically don't do that. I get a rough idea of how I want the session to go, but assume that my players are going to do something off-the-rails, and just wing it most of the time. Improv is my main tool in-game. It makes it so I'm never caught off-guard by something my players do, ruining a very neatly-prepared session and wasting a lot of time on my part.